The present invention relates generally to a protective switch which prevents damage to components in an electronic switching power converter and, more particularly, to a failsafe power-up/power-down switch which assures that the logic controlling the switching of bipolar power transistors passes through a known sequence of states upon energizing or de-energizing of the power source.
It is important to have logic in a complex system pass through a known sequence of states when the circuits are energized or de-energized from a power source. This not only insures proper start up operation of the circuit, but also prevents the occurence of potentially destructive states insofar as the circuit components are concerned. Thus, it is desirable to guarantee the system logic remains in a benign state until it is fully energized and ready for operation or until it is fully de-energized.
In the case of an electronic switching power converter, such as a brushless DC motor drive, having series connected bipolar power transistors between a high voltage DC source and ground, it is very important that both switches, and therefore both bipolar power transistors, not be turned on simultaneously. The critical time at which such a phenomenon can occur is during power-up or power-down of such devices; so there exists a definite need to assure that such a condition does not occur.